Astronomers Reveal Contents of Mysterious Black Hole Jets

Nov. 13, 2013 — An international team of astronomers has answered a long standing question about the enigmatic jets emitted by black holes, in research published today in the journal Nature.

Jets are narrow beams of matter spat out at high speed from near a central object, like a black hole.

"Although they have been observed for decades, we're still not sure what they are made of, or what powers them," ESO astronomer Dr María Díaz Trigo, lead author of the study, said.

The team studied the radio waves and X-rays emitted by a small black hole a few times the mass of the Sun. The black hole in question was known to be active, but the team's radio observations did not show any jets, and the X-ray spectrum didn't reveal anything unusual.

However, a few weeks later, the team took another look and this time saw radio emissions corresponding to the sudden appearance of these jets, and even more interestingly, lines had appeared in the X-ray spectrum -- the tell-tale signature of ordinary atoms -- around the black hole.

"Intriguingly, we found the lines were not where they should be, but rather were shifted significantly," Dr James Miller Jones from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), who led the radio observations, said.

The same effect occurs when a siren from a vehicle changes pitch as it moves towards or away from us, as the sound wave is shortened or lengthened by the movement.

"It led us to conclude the particles were being accelerated to fast speeds in the jets, one directed towards Earth, and the other one in the opposite direction," team member Dr Simone Migliari from the University of Barcelona said.

Dr Miller-Jones said this is the first strong evidence of such particles in jets from a typical small black hole.

"We've known for a long time that jets contain electrons, but haven't got an overall negative charge, so there must be something positively charged in them too," Dr Miller Jones said.

"Until now it wasn't clear whether the positive charge came from positrons, the antimatter 'opposite' of electrons, or positively charged atoms. Since our results found nickel and iron in these jets, we now know ordinary matter must be providing the positive charge."

Positively charged atoms are much heavier than the positrons astronomers thought might make up the jets, and therefore the jets can carry away far more energy from the black hole than previously confirmed.What's more, astronomers aren't sure whether the jets are powered by the spin of the rotating black hole itself, or whether they are instead launched directly from the disk of matter that surrounds the black hole.

"Our results suggest it's more likely the disk is responsible for channelling the matter into the jets, and we are planning further observations to try and confirm this," Dr Miller-Jones said. Using the X-ray data, the team also determined the jets were moving at 66% of the speed of light, or 198,000 km/s, the most accurate determination to date of the jet speed from a run-of-the-mill black hole that's a few times the mass of the Sun.

For their observations, the team used the European Space Agency's XMM-Newton satellite to observe X-ray emission from the black hole, as well as CSIRO's Australia Telescope Compact Array for the radio observations
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Better Batteries Through Biology? Modified Viruses Boost Battery Performance

Nov. 13, 2013 — MIT researchers have found a way to boost lithium-air battery performance, with the help of modified viruses.

Lithium-air batteries have become a hot research area in recent years: They hold the promise of drastically increasing power per battery weight, which could lead, for example, to electric cars with a much greater driving range. But bringing that promise to reality has faced a number of challenges, including the need to develop better, more durable materials for the batteries' electrodes and improving the number of charging-discharging cycles the batteries can withstand.

Now, MIT researchers have found that adding genetically modified viruses to the production of nanowires -- wires that are about the width of a red blood cell, and which can serve as one of a battery's electrodes -- could help solve some of these problems.

The new work is described in a paper published in the journalNature Communications, co-authored by graduate student Dahyun Oh, professors Angela Belcher and Yang Shao-Horn, and three others. The key to their work was to increase the surface area of the wire, thus increasing the area where electrochemical activity takes place during charging or discharging of the battery.

The researchers produced an array of nanowires, each about 80 nanometers across, using a genetically modified virus called M13, which can capture molecules of metals from water and bind them into structural shapes. In this case, wires of manganese oxide -- a "favorite material" for a lithium-air battery's cathode, Belcher says -- were actually made by the viruses. But unlike wires "grown" through conventional chemical methods, these virus-built nanowires have a rough, spiky surface, which dramatically increases their surface area.

Belcher, the W.M. Keck Professor of Energy and an affiliate of MIT's Koch Institute for Integrative Cancer Research, explains that this process of biosynthesis is "really similar to how an abalone grows its shell" -- in that case, by collecting calcium from seawater and depositing it into a solid, linked structure.

The increase in surface area produced by this method can provide "a big advantage," Belcher says, in lithium-air batteries' rate of charging and discharging. But the process also has other potential advantages, she says: Unlike conventional fabrication methods, which involve energy-intensive high temperatures and hazardous chemicals, this process can be carried out at room temperature using a water-based process.

Also, rather than isolated wires, the viruses naturally produce a three-dimensional structure of cross-linked wires, which provides greater stability for an electrode.

A final part of the process is the addition of a small amount of a metal, such as palladium, which greatly increases the electrical conductivity of the nanowires and allows them to catalyze reactions that take place during charging and discharging. Other groups have tried to produce such batteries using pure or highly concentrated metals as the electrodes, but this new process drastically lowers how much of the expensive material is needed.

Altogether, these modifications have the potential to produce a battery that could provide two to three times greater energy density -- the amount of energy that can be stored for a given weight -- than today's best lithium-ion batteries, a closely related technology that is today's top contender, the researchers say.

Belcher emphasizes that this is early-stage research, and much more work is needed to produce a lithium-air battery that's viable for commercial production. This work only looked at the production of one component, the cathode; other essential parts, including the electrolyte -- the ion conductor that lithium ions traverse from one of the battery's electrodes to the other -- require further research to find reliable, durable materials. Also, while this material was successfully tested through 50 cycles of charging and discharging, for practical use a battery must be capable of withstanding thousands of these cycles.

While these experiments used viruses for the molecular assembly, Belcher says that once the best materials for such batteries are found and tested, actual manufacturing might be done in a different way. This has happened with past materials developed in her lab, she says: The chemistry was initially developed using biological methods, but then alternative means that were more easily scalable for industrial-scale production were substituted in the actual manufacturing.

In addition to Oh, Belcher, and Shao-Horn, the work was carried out by MIT research scientists Jifa Qi and Yong Zhang and postdoc Yi-Chun Lu. The work was supported by the U.S. Army Research Office and the National Science Foundation
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Evidence of 3.5-Billion-Year-Old Bacterial Ecosystems Found in Australia

Nov. 12, 2013 — Reconstructing the rise of life during the period of Earth's history when it first evolved is challenging. Earth's oldest sedimentary rocks are not only rare, but also almost always altered by hydrothermal and tectonic activity. A new study from a team including Carnegie's Nora Noffke, a visiting investigator, and Robert Hazen revealed the well-preserved remnants of a complex ecosystem in a nearly 3.5 billion-year-old sedimentary rock sequence in Australia.

Their work is published in Astrobiology.

The Pilbara district of Western Australia constitutes one of the famous geological regions that allow insight into the early evolution of life. Mound-like deposits created by ancient photosynthetic bacteria, called stromatolites, and microfossils of bacteria have been described by scientists in detail. However, a phenomenon called microbially induced sedimentary structures, or MISS, had not previously been seen in this region. These structures are formed from mats of microbial material, much like mats seen today on stagnant waters or in coastal flats.

The team included Noffke, Hazen, Daniel Christian of Old Dominion University, and David Wacey of the University of Western Australia. They described various MISS preserved in the region's Dresser Formation. Advanced chemical analyses point toward a biological origin of the material. The Dresser MISS fossils resemble strongly in form and preservation the MISS from several other younger rock samples, such as a 2.9 billion-year-old ecosystem Noffke and her colleagues found in South Africa.

"This work extends the geological record of MISS by almost 300 million years," said Noffke, who is also a professor at ODU. "Complex mat-forming microbial communities likely existed almost 3.5 billion years ago."

The team proposes that the sedimentary structures arose from the interactions of bacterial films with shoreline sediments from the region.

"The structures give a very clear signal on what the ancient conditions were, and what the bacteria composing the biofilms were able to do," Noffke said.

MISS are among the targets of Mars rovers, which search for similar formations on that planet's surface. Thus, the team's findings could have relevance for studies of our larger Solar System as well
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Thin, Active Invisibility Cloak Demonstrated for First Time

Nov. 12, 2013 — Invisibility cloaking is no longer the stuff of science fiction: two researchers in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering have demonstrated an effective invisibility cloak that is thin, scalable and adaptive to different types and sizes of objects.

Professor George Eleftheriades and PhD student Michael Selvanayagam have designed and tested a new approach to cloaking -- by surrounding an object with small antennas that collectively radiate an electromagnetic field. The radiated field cancels out any waves scattering off the cloaked object. Their paper 'Experimental demonstration of active electromagnetic cloaking' appears today in the journalPhysical Review X.

"We've taken an electrical engineering approach, but that's what we are excited about," says Eleftheriades. "It's very practical."

Picture a mailbox sitting on the street. When light hits the mailbox and bounces back into your eyes, you see the mailbox. When radio waves hit the mailbox and bounce back to your radar detector, you detect the mailbox. Eleftheriades and Selvanyagam's system wraps the mailbox in a layer of tiny antennas that radiate a field away from the box, cancelling out any waves that would bounce back. In this way, the mailbox becomes undetectable to radar.

"We've demonstrated a different way of doing it," says Eleftheriades. "It's very simple: instead of surrounding what you're trying to cloak with a thick metamaterial shell, we surround it with one layer of tiny antennas, and this layer radiates back a field that cancels the reflections from the object."

Their experimental demonstration effectively cloaked a metal cylinder from radio waves using one layer of loop antennas. The system can be scaled up to cloak larger objects using more loops, and Eleftheriades says the loops could become printed and flat, like a blanket or skin. Currently the antenna loops must be manually attuned to the electromagnetic frequency they need to cancel, but in future they could function both as sensors and active antennas, adjusting to different waves in real time, much like the technology behind noise-cancelling headphones.

Work on developing a functional invisibility cloak began around 2006, but early systems were necessarily large and clunky -- if you wanted to cloak a car, for example, in practice you would have to completely envelop the vehicle in many layers of metamaterials in order to effectively "shield" it from electromagnetic radiation. The sheer size and inflexibility of the approach makes it impractical for real-world uses. Earlier attempts to make thin cloaks were not adaptive and active, and could work only for specific small objects.

Beyond obvious applications, such as hiding military vehicles or conducting surveillance operations, this cloaking technology could eliminate obstacles -- for example, structures interrupting signals from cellular base stations could be cloaked to allow signals to pass by freely. The system can also alter the signature of a cloaked object, making it appear bigger, smaller, or even shifting it in space. And though their tests showed the cloaking system works with radio waves, re-tuning it to work with Terahertz (T-rays) or light waves could use the same principle as the necessary antenna technology matures.

"There are more applications for radio than for light," says Eleftheriades. "It's just a matter of technology -- you can use the same principle for light, and the corresponding antenna technology is a very hot area of research.
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Clay May Have Been Birthplace of Life On Earth, New Study Suggests

Nov. 5, 2013 — Clay, a seemingly infertile blend of minerals, might have been the birthplace of life on Earth. Or at least of the complex biochemicals that make life possible, Cornell University biological engineers report in the Nov. 7 online issue of the journal Scientific Reports, published by Nature Publishing.

"We propose that in early geological history clay hydrogel provided a confinement function for biomolecules and biochemical reactions," said Dan Luo, professor of biological and environmental engineering and a member of the Kavli Institute at Cornell for Nanoscale Science.

In simulated ancient seawater, clay forms a hydrogel -- a mass of microscopic spaces capable of soaking up liquids like a sponge. Over billions of years, chemicals confined in those spaces could have carried out the complex reactions that formed proteins, DNA and eventually all the machinery that makes a living cell work. Clay hydrogels could have confined and protected those chemical processes until the membrane that surrounds living cells developed.

To further test the idea, the Luo group has demonstrated protein synthesis in a clay hydrogel. The researchers previously used synthetic hydrogels as a "cell-free" medium for protein production. Fill the spongy material with DNA, amino acids, the right enzymes and a few bits of cellular machinery and you can make the proteins for which the DNA encodes, just as you might in a vat of cells.

To make the process useful for producing large quantities of proteins, as in drug manufacturing, you need a lot of hydrogel, so the researchers set out to find a cheaper way to make it. Postdoctoral researcher Dayong Yang noticed that clay formed a hydrogel. Why consider clay? "It's dirt cheap," said Luo. Better yet, it turned out unexpectedly that using clay enhanced protein production.

But then it occurred to the researchers that what they had discovered might answer a long-standing question about how biomolecules evolved. Experiments by the late Carl Sagan of Cornell and others have shown that amino acids and other biomolecules could have been formed in primordial oceans, drawing energy from lightning or volcanic vents. But in the vast ocean, how could these molecules come together often enough to assemble into more complex structures, and what protected them from the harsh environment?

Scientists previously suggested that tiny balloons of fat or polymers might have served as precursors of cell membranes. Clay is a promising possibility because biomolecules tend to attach to its surface, and theorists have shown that cytoplasm -- the interior environment of a cell -- behaves much like a hydrogel. And, Luo said, a clay hydrogel better protects its contents from damaging enzymes (called "nucleases") that might dismantle DNA and other biomolecules.

As further evidence, geological history shows that clay first appeared -- as silicates leached from rocks -- just at the time biomolecules began to form into protocells -- cell-like structures, but incomplete -- and eventually membrane-enclosed cells. The geological events matched nicely with biological events.

How these biological machines evolved remains to be explained, Luo said. For now his research group is working to understand why a clay hydrogel works so well, with an eye to practical applications in cell-free protein production.

Luo collaborated with professor Max Lu of the Australian Institute for Bioengineering and Nanotechnology at the University of Queensland in Australia. The work was performed at the Cornell Center for Materials Research Shared Facilities, supported by the National Science Foundation.

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How Pigeons May Smell Their Way Home

Nov. 5, 2013 — Homing pigeons, like other birds, are extraordinary navigators, but how they manage to find their way back to their lofts is still debated. To navigate, birds require a 'map' (to tell them home is south, for example) and a 'compass' (to tell them where south is), with the sun and the earth's magnetic field being the preferred compass systems. A new paper provides evidence that the information pigeons use as a map is in fact available in the atmosphere: odors and winds allow them to find their way home.

The results are now published inBiogeosciences, an open access journal of the European Geosciences Union (EGU).

Experiments over the past 40 years have shown that homing pigeons get disoriented when their sense of smell is impaired or when they don't have access to natural winds at their home site. But many researchers were not convinced that wind-borne odors could provide the map pigeons need to navigate. Now, Hans Wallraff of the Max Planck Institute for Ornithology in Seewiesen, Germany, has shown that the atmosphere does contain the necessary information to help pigeons find their way home.

In previous research, Wallraff collected air samples at over 90 sites within a 200 km radius around a former pigeon loft near Würzburg in southern Germany. The samples revealed that the ratios among certain 'volatile organic compounds' (chemicals that can be a source of scents and odors) in the atmosphere increase or decrease along specific directions. "For instance, the percentage of compound A in the sum A+B or A+B+C+D increases the farther one moves from north to south," Wallraff explains.

These changes in compound ratios translate into changes in perceived smell. But a pigeon that has never left its loft does not know in what directions what changes occur -- unless it has been exposed to winds at its home site.

At home, a bird is thought to associate certain smells with particular wind directions. "If the percentage of compound A increases with southerly winds, a pigeon living in a loft in Würzburg learns this wind-correlated increase. If released at a site some 100 km south of home, the bird smells that the ratio of compound A is above what it is on average at its loft and flies north," Wallraff explains. To use an analogy, a person in Munich could smell an Alpine breeze when there is wind blowing from the south. When displaced closer to the mountains, they would detect a strong Alpine scent and remember that, at home, that smell is associated with southerly winds: the person would know that, roughly, they needed to travel north to find home.

But this explanation of how pigeons might use wind-borne odors to find their loft was just a hypothesis: Wallraff still needed to prove that the atmosphere does indeed contain the basis of the map system pigeons need to navigate. In the new Biogeosciences paper, he develops a model showing that 'virtual pigeons' with only knowledge of winds and odors at home, can find their way back to their lofts by using real atmospheric data.

"My virtual pigeons served as tools to select those volatile compounds whose spatial distributions, combined with variations dependent on wind direction, were most suitable for homeward navigation," explains Wallraff.

The model uses an iterative approach to imitate animal evolution by introducing random mutations in the virtual pigeons, making them most sensitive to those volatile compounds that are most effective for navigation. By selecting the best mutations in the course of thousands of generations, the model creates virtual pigeons capable of finding their bearings as well as real pigeons, showing that even inexperienced birds could use atmospheric information for navigation. The findings present a missing piece in the puzzle of homing pigeon navigation, confirming that winds and odors can indeed work as a map system.

"Work with real pigeons was the beginning of the story. In this research, I wanted to find out whether and in what way the chemical atmosphere fulfills the demands for avian navigation. Eventually, to identify the chemical compounds birds actually use for home-finding, we will need real birds again. But this is far in the future.
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How Common Are Habitable Planets? One in Five Sun-Like Stars May Have Earth-Size, Potentially Habitable Planets

Nov. 4, 2013 — NASA's Kepler space telescope, now crippled and its four-year mission at an end, nevertheless provided enough data to answer its main research question: How many of the 200 billion stars in our galaxy have potentially habitable planets?

Based on a statistical analysis of all the Kepler observations, University of California, Berkeley, and University of Hawaii, Manoa, astronomers now estimate that one in five stars like the sun have planets about the size of Earth and a surface temperature conducive to life.

Given that about 20 percent of stars are sun-like, the researchers say, that amounts to several tens of billions of potentially habitable, Earth-size planets in the Milky Way Galaxy.

"When you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing," said UC Berkeley graduate student Erik Petigura, who led the analysis of the Kepler data.

"It's been nearly 20 years since the discovery of the first extrasolar planet around a normal star. Since then, we have learned that most stars have planets of some size orbiting them, and that Earth-size planets are relatively common in close-in orbits that are too hot for life," said Andrew Howard, a former UC Berkeley post-doctoral fellow who is now on the faculty of the Institute for Astronomy at the University of Hawaii. "With this result, we've come home, in a sense, by showing that planets like our Earth are relatively common throughout the Milky Way Galaxy."

Petigura, Howard and Geoffrey Marcy, UC Berkeley professor of astronomy, will publish their analysis and findings this week in the online early edition of the journal Proceedings of the National Academy of Sciences.

Earth-size may not mean habitable

"For NASA, this discovery is really important, because future missions will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are," Howard said. "An abundance of planets orbiting nearby stars simplifies such follow-up missions."

The team cautioned that Earth-size planets in orbits about the size of Earth's are not necessarily hospitable to life, even if they reside in the habitable zone around a star where the temperature is not too hot and not too cold.

"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive. Others may have rocky surfaces that could harbor liquid water suitable for living organisms," Marcy said. "We don't know what range of planet types and their environments are suitable for life."

Last week, however, Howard, Marcy and their colleagues provided hope that many such planets actually are rocky and could support liquid water. They reported that one Earth-size planet discovered by Kepler -- albeit, a planet with a likely temperature of 2,000 Kelvin, which is far too hot for life as we know it -- is the same density as Earth and most likely composed of rock and iron, like Earth.

"This gives us some confidence that when we look out into the habitable zone, the planets Erik is describing may be Earth-size, rocky planets," Howard said.

Transiting planets

NASA launched the Kepler space telescope in 2009 to look for planets outside the solar system that cross in front of, or transit, their stars, which causes a slight diminution -- about one hundredth of 1 percent -- in the star's brightness. From among the 150,000 stars photographed every 30 minutes for four years, NASA's Kepler team reported more than 3,000 planet candidates. Many of these are much larger than Earth -- ranging from large planets with thick atmospheres, like Neptune, to gas giants like Jupiter -- or in orbits so close to their stars that they are roasted.

To sort them out, Petigura and his colleagues are using the Keck telescopes in Hawaii to obtain spectra of as many stars as possible. This will help them determine each star's true brightness and calculate the diameter of each transiting planet, with an emphasis on Earth-diameter planets.

Independently, Petigura, Howard and Marcy focused on the 42,000 stars that are like the sun or slightly cooler and smaller, and found 603 candidate planets orbiting them. Only 10 of these were Earth-size, that is, one to two times the diameter of Earth and orbiting their star at a distance where they are heated to lukewarm temperatures suitable for life. The team's definition of habitable is that a planet receives between four times and one-quarter the amount of light that Earth receives from the sun.

A census of extrasolar planets

What distinguishes the team's analysis from previous analyses of Kepler data is that they subjected Petigura's planet-finding algorithms to a battery of tests in order to measure how many habitable zone, Earth-size planets they missed. Petigura actually introduced fake planets into the Kepler data in order to determine which ones his software could detect and which it couldn't.

"What we're doing is taking a census of extrasolar planets, but we can't knock on every door. Only after injecting these fake planets and measuring how many we actually found could we really pin down the number of real planets that we missed," Petigura said.

Accounting for missed planets, as well as the fact that only a small fraction of planets are oriented so that they cross in front of their host star as seen from Earth, allowed them to estimate that 22 percent of all sun-like stars in the galaxy have Earth-size planets in their habitable zones.

"The primary goal of the Kepler mission was to answer the question, 'When you look up in the night sky, what fraction of the stars that you see have Earth-size planets at lukewarm temperatures so that water would not be frozen into ice or vaporized into steam, but remain a liquid, because liquid water is now understood to be the prerequisite for life?'" Marcy said. "Until now, no one knew exactly how common potentially habitable planets were around sun-like stars in the galaxy."

All of the potentially habitable planets found in the team's survey are around K stars, which are cooler and slightly smaller than the sun, Petigura said. But the researchers' analysis shows that the result for K stars can be extrapolated to G stars like the sun. Had Kepler survived for an extended mission, it would have obtained enough data to directly detect a handful of Earth-size planets in the habitable zones of G-type stars.

"If the stars in the Kepler field are representative of stars in the solar neighborhood, … then the nearest (Earth-size) planet is expected to orbit a star that is less than 12 light-years from Earth and can be seen by the unaided eye," the researchers wrote in their paper. "Future instrumentation to image and take spectra of these Earths need only observe a few dozen nearby stars to detect a sample of Earth-size planets residing in the habitable zones of their host stars."

In January, the team reported a similar analysis of Kepler data for scorched planets that orbit close to their stars. The new, more complete analysis shows that "nature makes about as many planets in hospitable orbits as in close-in orbits," Howard said.

The research was funded by UC Berkeley and the National Science Foundation, with the assistance of the W. M. Keck Observatory and NASA.

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